 Use
the 2-wire PT and CT Transmitters models BPT and BCT. Install them in the
field near the current and voltage transformers, and supply driving power
from current loop supply unit at the control section of DCS in the central
control station.
Merits:
1) By installing the signal conditioner in the field, you do not have to
lead AC output from transformers as far as to control panel of the DCS:
there is no special consideration on cables required for AC transmission
or their installation.
2) You can get standard 4 to 20 mAdc output from the signal conditioner:
with L-Unit PT and CT Transducers models LPNE/LCNE which take their driving
power from input loop, you can only have a signal such as 0 to 1 mAdc, the
lower range output of which equals zero; thus receiving 0 mA output, you
cannot be sure if a leadwire breaks or opens.
3) The signal conditioners installed in the field are more independent from
the central DCS than those installed in racks at the control section of
the DCS: users can freely design the field system only if current loop supply
units are in the DCS. |
I
want to monitor AC current and voltage on main power supply lines via transformers.
But I have not much space for installation of signal conditioners and their
wiring. I do not want to have any additional external power supply.
